1. Field of the Invention
This invention is directed to a lightweight underwater acoustic reflector with enhanced performance and to a novel method for constructing the same.
2. Description of the Prior Art
Many approaches have been developed to minimize the transmission or reflection or waterborne acoustic energy with the introduction of sound ranging and detection. Since the advent of the submarine, the ingenuity of designers has been particularly drawn upon to frustrate the detection capabilities of an adversary by making or otherwise obliterating the reflection of a probing acoustic interrogation signal and also sound radiated by a vessel. The change of hull configuration has been utilized to reduce the reflected signature, however, this change has not been very successful since weight and pressure considerations had to be unduly compromised and the problem of evasion by the vessel was necessarily left to a commander's discretion. Bubbles have also been used to acoustically decoy or mask a submersible vessel, however, this method is only partially effective as the bubbles create a reflective air column that draws attention or tends to inadequately clothe a submersible from acoustic probing. Acoustic coatings bonded on to exposed surfaces of a submersible have also been used. Other items, such as, panels, various types of coatings and compliant layers have been attached onto the hulls of undersea craft. Most have been not entirely successful because of difficulty in applying them to and to retaining them on the exposed surfaces, often they do not conform readily to irregular contours and often are unstable in a submersible's environment with temperature and pressure variations. Many also experience limited time usefulness due to fatigue and failure. Further, for use underwater they are very expensive, most deteriorate rapidly in a seawater environment, they are vulnerable to damage during docking, and they exhibit inconsistent frequency responses over wide spectra.
One recent attempt to overcome the limitations imposed by the prior art is illustrated in U.S. Pat. No. 4,450,544 wherein the inventors illustrate an acoustical energy absorbing baffle for minimizing sound reflection and providing isolation from noise producing sources wherein the acoustical energy absorbing baffle has a pair of restricted orifice screens rigidly secured in parallel spaced relation by a lattice stiffener, said stiffener assembly is immersed in a viscous fluid contained within a tank sealed with an elastic diaphragm. Incident acoustical energy is transmitted through the diaphragm and translated into energy absorbing motion of the fluid through the restrictive screens. The fluid and screen are designed to match the impedance of water. An acoustically compliant layer is coupled to the fluid to augment fluid particle velocity through the screens and thus to further absorb energy. The viscous fluid utilized is a silicon oil. However, no baffle enhancement effect is obtained at the most desired and necessary low frequencies.